Power control is an important technique for a CDMA mobile communication system. Purpose of the power control is to overcome near-far effect in the way that a system not only keeps higher communication quality, but also operates without interference to other subscribers sharing the same channel. In the 3G mobile communication system, the power control uses decision feedback mode, which works as follows. The receiving end B measures signal-to-interference ratio (SIR) of a received signal, then, the measured SIR value is compared with a SIR threshold-value to generate a Transmit Power Control (TPC) command. The TPC is sent to the transmitting end A, and A adjusts the transmitting power based on the received TPC command. Usually, the adjustment happens once for a time-slot.
In a wideband CDMA (WCDMA) system, a multiple time-slot TPC control method has been defined (reference to 3GPP TS25.211). In this method, the receiving end B also sends back a TPC command to the transmitting end A during every time-slot. However, during every N time-slot, from the 1st to the (N−1)th, the transmitting end A does not adjust the transmitting power with the TPC command, but at the Nth time-slot, the transmitting end A adjusts the transmitting power based on the N TPC commands. In this case, the N time-slots are seen as a power control group. The specific procedure is as the following:
During the first N−1 time-slots, the receiving end B measures SIR values of the received signal, and compares with a SIR threshold-value to generate a TPC command, which is then sent back to the transmitting end A. During this N−1 period, the transmitting end A receives and stores the feedback TPC commands, but does not adjust the transmitting power.
At the Nth time-slot, after having been received the Nth TPC command, the transmitting end A executes the followings:                (1) If N time-slots TPC commands are all “1”, then the transmitting power is increased;        (2) If N time-slots TPC commands are all “0”, then the transmitting power is decreased;        (3) Otherwise, the transmitting power will not be adjusted.        
Since the TPC command is obtained by hard decision, and there are no encoding and decoding during transmission, the TPC command has a higher error code. Consequentially, with this method, the power control result has a big inaccuracy.